In vertebrate outer hair cells, synaptic inhibition is achieved by the activation of nicotinic (ionotropic) acetylcholine (ACh) receptors that usually mediate excitatory postsynaptic responses else where in the nervous system. Calcium (Ca++) influx through these ACh receptors leads to activation of calcium dependent potassium channels. This proposal aims to explore the intracellular pathways that couple the ionotropic hair cell ACh receptors to inhibition. A combination of electrophysiology and molecular biology techniques will be used to test whether an IP3-sensitive calcium store may be involved in such a process. Since phospholipase C (PLC) catalyses the synthesis of IP3, the role of PLC in cholinergic inhibition will be examined next by employing pharmacological agents. RT-PCR and immunohistochemistry will used to determine the pattern of expression of the different PLC sub-types in the cochlea. Data from this research will help elucidate the molecular mechanisms by which ACh released from the olivo-cochlear bundle mediates hair cell inhibition.